Effect of Syngas (H
/CO) on SI Engine Knock under Boosted EGR and Lean Conditions
Syngas (synthesis gas) aided combustion from various fuel reforming strategies is of increasing interest in boosted lean burn SI engines due to its impact on dilution tolerance and knock resistance. Due to the interest in reformed fuels, more concrete understanding of how to leverage syngas supplementation under various lean conditions is essential to optimize engine performance and derive the most benefit from the availability of syngas in the combustion process. While the impact of syngas supplementation on combustion stability has been studied adequately, detailed understanding of the impact of syngas on knocking is still limited. Hence, this study investigates the effect of syngas (H2/CO) addition on knock tendency under boosted EGR (Exhaust Gas Recirculation) and air diluted conditions. Syngas amount is controlled on an energy basis from 0% to 15% to compare the difference between EGR and air dilution. At first, several knock quantification methods are compared, and a suitable knock index and guideline are selected. Knocking tendencies with respect to the frequency, combustion phasing, and burn duration are analyzed based on observed engine knock. Also, the thermal efficiency and emissions difference are discussed as well. The results show that with increasing the syngas supplementation ratio, knocking is strongly suppressed, and the effect is more beneficial with EGR dilution than with air dilution.